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INTRODUCTION

Disorders of the autonomic nervous system (ANS) are being recognized in increasing numbers of infants, children, and adolescents. Autonomic dysfunction may be central, or may involve the peripheral ANS, which includes sympathetic and parasympathetic components, as well as the enteric ANS and the adrenal glands. It is important to understand that autonomic symptoms are the manifestations of efferent systems outflow, which occurs in response to afferent systems input that may have been modulated by the central ANS.

Autonomic dysfunction may manifest as paroxysmal events in the form of apnea, syncope, autonomic storms, and autonomic symptoms accompanying headaches or epileptic seizures. Autonomic dysfunction may also manifest as subacute or chronic conditions that are either functional in nature or caused by genetic, traumatic, metabolic, vascular, neoplastic, paraneoplastic, or autoimmune disorders.

Dysautonomia may be defined as a change in the ANS that adversely affects health. However, the diagnosis of dysautonomia should really be limited to a set of disease states wherein a detectable abnormality of the ANS is critical to the pathogenesis. Diabetic autonomic neuropathy is a form of dysautonomia, whereas recurrent syncope or frequent lightheadedness in an adolescent with chronic fatigue represents autonomic dysfunction. Likewise, a child with migraine and autonomic symptoms of palpitations, dizziness, and pupillary changes has autonomic dysfunction, not dysautonomia. Disease-related dysautonomia generally has a worse long-term prognosis than do functional autonomic dysfunction syndromes. Hereditary sensory autonomic neuropathies (HSAN) types II, III, and IV are examples of dysautonomia.

Autonomic dysfunction may involve any organ system, such as Horner syndrome, functional gastrointestinal disorders, and neurogenic bladder. Disorders of orthostatic intolerance (OI) in the form of initial orthostatic hypotension (IOH), syncope, or near syncope, or chronic OI in the form of postural tachycardia syndrome (POTS) are quite common in adolescents. Chronic orthostatic hypotension (OH) is rare in children. Disorders of sweating may be related to a congenital disorder, autonomic neuropathy, or functional syndromes, or may be secondary to systemic conditions. Genetic dysautonomia is related to abnormal development of the peripheral or central ANS and typically involves dysfunction in neurotransmitters. An example is Riley-Day syndrome, or HSAN type III.

CLINICAL EVALUATION

Taking a Relevant History

The evaluation of autonomic dysfunction starts with a comprehensive history that includes specific attention to symptoms related to the ANS (Table 568-1). Orthostatic intolerance is defined as the symptoms or signs of presumed cerebral hypoperfusion or sympathetic activation upon arising or during upright posture that are relieved by recumbence. It is important to document when the symptoms of autonomic dysfunction began. It is also important to identify any triggers or antecedent events, such as infection, surgery, trauma, excessive exercise, onset of puberty and menarche, menstrual abnormalities, starting new medications, or prolonged bed rest. A thorough history of nutritional, fluid, and salt intake is important as well. Moreover, it is helpful to note whether symptoms are mild or ...

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